1. Field of the Invention
The present invention relates to a work transfer apparatus and, more particularly, to a work transfer apparatus which is constructed to move a work to an operating position while transferring the work by means of a conveyor, performs predetermined processing at this operating position, and discharges the processed work.
2. Description of Related Art
Component mounters are widely used in order to mount components on circuit boards and fabricate electronic circuits. A component mounter is provided with a suction nozzle at one end of a mount head, and causes this suction to attract a component by suction and moves the suction nozzle to a position above a predetermined mounting position on a circuit board by moving the suction nozzle in the X-axis and Y-axis directions relative to the circuit board. Then, the component mounter moves the suction nozzle down toward the circuit board, and mounts the attracted component on the circuit board at a predetermined position thereof.
This component mounter needs to sequentially transfer circuit boards to a mounting position below the mount head, and is provided with a board transfer system for this purpose. Board transfer systems are generally classified into two kinds: that is to say, a type which performs component mounting by moving the position of a board together with a conveyor, as represented by a rotary machine, and a type which performs component mounting with a board fixed in position. However, in the first type as well, since boards connected to conveyors fixed at preceding and succeeding positions need to be replaced when boards are to be replaced, the transfer of boards is under the same conditions except the time necessary for this connection is added.
As described above, a conveyor for transferring circuit boards on which components are to be mounted in the component mounter is made of three kinds of conveyors which are a conveyor provided at a component mounting position and conveyors provided at positions preceding and succeeding the component mounting position. The outline of operation to be started during the state in which the next board is waiting while components are being mounted on a board will be described below.
a. After the mounting of components on a board has been completed, the board is released from a clamp, a backup, positioning pins and the like.
b. The conveyor provided at the component mounting position starts to move, and the board on which the components have been mounted starts to move.
c. When it is detected that the rear end of the board has come out of the conveyor provided at the component mounting position, a stopper moves upward.
d. After it is confirmed that the stopper has moved up, the conveyor preceding the component mounting position is started to initiate loading the next board.
e. Before the board reaches the stopper, the conveyor is decelerated by means of a sensor, a timer and the like, and the board is made to stop in the state of being lightly pressed against the stopper and the conveyor is also made to stop.
f. A positioning pin is moved upward to perform clamping and backup, thereby completing the replacement of the boards.
A beam-transfer board transfer system which is said to be shorter in board replacement time than the above-mentioned board transfer system made of conventional conveyors are disclosed in, for example, Japanese Laid-Open Patent JP-A-6-336351 and Japanese Laid-Open Patent JP-A-2-229499. This system is shorter in the time required for replacement of boards than the above-mentioned conveyor system. Similarly to the conveyor system, this beam-transfer system is provided with three kinds of conveyors. Incidentally, a conveyor provided at an intermediate mounting position only supports a board and generally does not have the ability to move a board autonomously. The beam-transfer system has a stroke equal to a maximum of the length of a board in the flowing direction of boards, and includes a beam mechanism having two board feed claws. The outline of operation to be started during the state in which the next board is waiting while components are being mounted on a board will be described below.
a. After the mounting of components on a board has been completed, the board is released from a clamp, a backup, positioning pins and the like.
b. Two board feed claws are inserted into a position where they can press the rear end of the board on which the components have been mounted and the rear end of the next board, by a method such as rotating a beam provided outside a conveyor.
c. The beam starts to move in the flowing direction of boards, and discharges the board on which the components have been mounted, from a component mounting area, and at the same time completes the operation of transferring the next board to a component mounting position.
d. A positioning pin is moved upward, and while the positioning pin is being made to perform clamping and backup, the claws are retracted and the beam returns to its original position, whereby the replacement of the boards is completed.
This beam-transfer system is considered to be theoretically capable of completing replacement of boards in the shortest time because both boards are moved at the same time. However, as shown by the fact that the beam-transfer system is not used as a normal system, the beam-transfer system has a number of disadvantages. The disadvantages are as follows.
a. In the case where discharging and loading cannot be performed at the same time, the discharging of a board on which components are mounted is first completed, and after a beam has been returned, claws have to be inserted after the next incoming board. As a result, there are cases where the beam-transfer system becomes slower than ordinary systems.
b. The beam-transfer system has the disadvantage of being large sized and difficult to install, for reasons such as: since two claws are integrated in the form of being separated from each other by a distance equal to a maximum board length, insertion and retraction of the claws is necessary and the beam has a stroke equal to a maximum board length.
c. Since two boards need to be pressed by the beam at the same time, the position of the claws needs to adjusted according to the size of boards.
The above-mentioned problem a in particular may be a fatal disadvantage even if the demerits of the other problems are accepted in order to adopt the beam-transfer system to shorten component replacement time.    [Patent Document 1] Japanese Patent Application publication (KOKAI) No. Hei 6-336351    [Patent Document 2] Japanese Patent Application publication (KOKAI) No. Hei 2-229499    [Patent Document 3] Japanese Patent Application publication (KOKAI) No. Hei 11-163595    [Patent Document 4] Japanese Patent Application publication (KOKAI) No. Hei 3-214798    [Patent Document 5] Japanese Patent Application publication (KOKAI) No. Hei 4-291800    [Patent Document 6] Japanese Patent Application publication (KOKAI) No. 2001-144494